The 3GPP (The 3rd Generation Partnership Project), which is a group for standardization of a mobile communication system, has been working to specify an EPS (Evolved Packet System) described in following Non-Patent Document 1 as a next-generation mobile communication system, and has made a study on a home base station that is a small-sized base station arranged in a house or the like as a component apparatus of the EPS.
The home base station constructs a small-scaled wireless cell called a femto-cell, and using a wireless access technology same as a normal eNB (eNodeB: base station), houses UE (User Equipment: mobile terminal apparatus). In addition, by connecting to a core network of a mobile communication system via a broadband line, it is possible to relay communication data of the UE that is housed.
Further, following Non-Patent Document 2 discloses architecture candidates for realizing local IP access (LIPA: Local IP Access) in a home base station. The local IP access is a function that provides UE with direct connectivity to a network such as a home IP network to which the home base station is connected directly (hereinafter, referred to as a “home network”), so that the UE becomes possible to communication with other information terminal (for example, such as a digital video recorder or a printer) being connected to the home network not via a core network of a mobile communication system.
Moreover, as one of the architecture candidates for realizing local IP access disclosed in Non-Patent Document 2, it is proposed to arrange a PGW (Packet data GW) defined in Non-Patent Document 1 in the home base station.
The PGW is an apparatus that performs assignment of an IP address to the UE as well as functions as a gateway to an external PDN (Packet Data Network: packet communication network) such as the Internet, and in the architecture candidates that are disclosed, it is proposed to cause the home base station to function as a gateway apparatus to the home network by arranging a subset (pared-down version) of the PGW called an L-PGW in the home base station.
The femto-cell constituted by individual home base stations has a radio wave covering range limited compared to that of a normal macro-cell. Therefore, in order to connect to a home network (specifically, intranet or the like) using local IP access under an environment of an office, a school or the like, a plurality of home base stations equipped with an L-PGW are arranged in the home network so that a wider area is able to be covered compared to the case of being in a home, and each UE is to be connected to an adjacent home base station.
However, according to a conventional technology described in Non-Patent Document 1, a PGW assigns an IP address to UE, and all communication data received by the UE is transferred through the PGW serving as a gateway apparatus. In addition, change of a connecting destination PGW is not performed to continue a communication session even at the time of handover.
Accordingly, even when the UE moves (executes handover) between a plurality of home base stations equipped with an L-PGW while performing communication by local IP access under the above-described environment of an office, a school or the like, in order to continue the communication session, it is impossible to switch the connecting destination L-PGW so that communication is performed via the L-PGW assigning an IP address to this UE at all times, resulting in causing of a redundant communication path.
On the other hand, when the connecting destination L-PGW is switched to optimize a communication path, the UE has no choice but to change the IP address used for the communication, it was therefore impossible to continue the communication session at the time of handover.
Moreover, Non-Patent Document 3 discloses a method for switching a connecting destination L-PGW while maintaining a communication session at the time of handover by expanding the conventional technology described in Non-Patent Document 1.
According to the method described in Non-Patent Document 3, using the procedure defined in the IETF RFC4861, the L-PGW equipped in the home base station carries out proxy transmission of neighbor advertisement including an IP address of UE and a MAC address of the home base station into a home network (hereinafter, referred to as Proxy Neighbor Advertisement processing), and carries out a proxy reception of communication data addressed to the UE, which is transmitted into the home network, for transferring to the UE.
In addition, when it is required to switch a connecting destination L-PGW in conjunction with handover processing or service request processing (that is processing in which UE that has transited to an idle mode moves to an adjacent base station again to resume communication) of the UE, on the initiative of an MME (Mobile Management Entity) serving as a position managing apparatus in a core network, an IP address that has been used by the UE before switching is notified to a switching destination L-PGW and start of Proxy NA processing is instructed, thereby realizing maintenance of a communication session.